The real tragedy occurs when someone is intellectually well-endowed but, because of emotional stumbling blocks, is incapable of making the sorts of contributions to society—and to his or her own life—that might otherwise result from those superior mental powers.
The last sentence，“that might otherwise result from those superior mental powers”，how to understand it？

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It means, if it wasn't for the "intellectually well-endowed people"'s "emotional stumbling blocks" (less developed and wide reaching emotional capabilities and understanding) then they would be able to make different, and possibly more helpful and impactful, contributions to society.

"might otherwise" means "if circumstances were different"

Because they have "superior mental powers" they have the opportunity to do amazing things (more than other people of a more "normal" level of intelligence) but they can't fulfill the full potential of it, because of the lack of emotional understanding